In 3GPP-LTE advanced, Coordinated Multi-Point Transmission (CoMP) is proposed as a key technology for further improving cell-edge performance. For uplink CoMP, one of the focused scenarios is the heterogeneous network scenario defined by 3GPP. A key feature in this scenario is the Decoupled DL-UL for some UEs, e.g., the UE as shown in FIG. 1 where an exemplary decoupled DL-UL scenario in the heterogeneous network is illustrated. In particular, as the Macro cell A has much higher transmission power than the Pico cell B, the coverage is different for the Macro cell A and the Pico cell B. For the UE located in the Macro cell coverage but at the coverage boundary between the Macro cell A and the Pico cell B, the received downlink signal from the Macro cell A is stronger than that from the Pico cell B. Hence the UE is associated with the Macro cell A and receives downlink signals from the Macro cell A. While for the uplink, since the UE is closer to the Pico cell B than the Macro cell A, it is better to select Pico cell B as the reception point, in order to reduce the transmit power of the UE and the interference to other normal UEs in the Pico cell B. Therefore, for this UE, the downlink serving cell is the Macro cell A but the uplink serving cell is the Pico cell B.
In the decoupled DL-UL scenario, it is up to Macro base station to manage DL transmission, yet Pico base station is in charge of UL transmission. If any backhaul connection (good, less than ˜0.5 ms latency; medium, ˜5 ms latency; poor, ˜50-100 ms latency) between the Macro base station and the Pico base station is considered, for example, when a slow backhaul connection is used, it is hard to support instantaneous information exchange between Macro base station and Pico base station, thus, DL-UL separation is implemented between Macro base station (DL) and Pico base station (UL). Due to this, physical uplink control channel (PUCCH) format 1a/1b/2/2a/2b/3 (including HARQ-ACK/NACK(A/N) and/or CQI) corresponding to the downlink transmission is to be received by Macro base station, and the Transmission power of UE shall be large enough to reach the Macro base station. While the scheduling request (D-SR and RA-SR) using PUCCH format 1 corresponding to the UL transmission is to be received by the Pico base station, and it shall reach the Pico base station, which means a low Transmission power of the UE to reduce the interference to other normal UEs (i.e., of which both DL and UL connections are served by the Pico cell) in the Pico cell.
If there is only D-SR transmitted in one subframe, it is OK for the Pico base station to receive it. However, 1) if 1 or 2 bits HARQ-ACK/NACK feedback and positive D-SR are to be transmitted in the same subframe, HARQ-ACK/NACK will be transmitted on D-SR's resource using PUCCH format 1a/1b; or 2) if up to 10-bit HARQ-ACK/NACK and 1-bit positive D-SR for FDD or 20-bit HARQ-ACK/NACK and 1-bit positive D-SR for TDD are transmitted in the same subframe, HARQ-ACK/NACK and D-SR are jointly encoded and PUCCH format 3 is used. Both PUCCH format 1a/1b and format 3 have to reach Macro base station, which means the Transmission power will be larger than that necessary to reach the Pico base station, so that it will 1) cause a strong interference to the D-SR monitoring of other normal UEs in the Pico cell in format 1a/1b case above. 2) the Pico base station will fully miss the D-SR information in format 3 as described above. Because the Pico base station doesn't know there is HARQ-ACK/NACK in this subframe, it will only monitor the D-SR resource instead of the resource of format 3.